Cutting head for a brush cutter, edge trimmer or similar

ABSTRACT

A cutting head for a brush cutter, edge trimmer or similar, the head comprises a passageway ( 112 ) for a cutter string ( 300 ) and at least one curved surface ( 120 ) for supporting the string, the surface extending between an exit region ( 115 ) for said string from said passageway and a peripheral region of the head. According to the invention, the passageway extends (A) in a manner that is offset from an axis of rotation (C) of the head so as to present an inside edge constituted by its edge closest to said axis of rotation, said inner edge corresponding to a trailing edge of the string while the head is rotating, and the curved portion extends from said inner edge. This serves to reduce the radius of curvature of the curved portion without needing to increase the diameter of the head.

The present invention concerns, in general the field of devices forcutting vegetation, such as brush cutters, edge trimmers, etc.

In this type of device, one or more cutting strings, unwound from areserve or in the form of individual strands, are solidly attached to acutting head driven in rotation by a motor driving the device, whileextending substantially radially in relation to the axis of rotation.

In basic implementations, the string outlet passageways are often formedby metallic or similar eyelets mounted on a peripheral surface of thehead and through them respective strands of string emerged from thehead.

While the device is in use, with the cutting head spinning at highspeed, the cutter string can be subjected to high levels of stress, inparticular by robust pieces of vegetation (trunks, etc.). or byobstacles (rocks, etc.). Under such circumstances, the string tends todepart from the radial direction it would normally occupy under theeffect of centrifugal force. As a result, the string is subjected tobending in the vicinity of the eyelet at levels that are extremely highboth in amplitude and in frequency, and very often the string breaks inthis region.

This requires the operator either to replace the string (when individualstrands of string are used), or else to deliver a new length of stringfrom a supply (a reel) situated inside the head, which operation is madeall the more difficult by the string breaking in the vicinity of theeyelet, thereby preventing it from being directly accessible to theoperator's fingers.

This operation is thus fiddly to perform in either case.

Cutting heads have also been developed in which curved string-supportportions are provided on either side of a string outlet so as to limitthe bending stresses to which the string is subjected when it isstressed as described above. This does indeed reduce stress on thestring, and it breaks less frequently. Documents . . . give examples ofheads fitted with such curved portions.

It should be observed that those prior art curved portions are effectivewith circular section polyamide strings of small diameter. Such stringsbend easily to follow the curve of a curved portion without beingsubjected to excessive fatigue.

In contrast, such curved portions become much less effective with cutterstrings for rougher work (clearing undergrowth, cutting very long grass,etc.), i.e. with strings of larger section and/or provided with specialarrangements (such as teeth, harder material in the cutting zone,projections or indentations for reducing noise, etc.). The string canbend much less without being subjected to fatigue, and the string doesnot manage to follow the curved portion without suffering such fatigue.

In parallel, it is not possible to increase the radius of curvature ofsuch curved portions without significantly increasing the diameter ofthe cutting head, and that is undesirable for reasons of size, weight,and expense, in particular. Given that it is necessary to provide,between the axis of rotation of the head and its periphery, both thecurved portions and mounting arrangements for the string (blockers orsinuous paths, particularly for individual strands, a supply reel whenan unreeling mechanism is provided), the curved portions can only have aradius of curvature that is relatively small.

The present invention seeks to mitigate those limitations of the priorart and to propose a cutting head in which the string outlet curvedportion(s) can present a small radius of curvature (and thus one or moreradii of curvature that are increased), without it being necessary toincrease the diameter of the head correspondingly.

For this purpose, the invention provides a cutting head for brushcutter, edge trimmer or similar, the head being of the type including apassageway for a cutter string and at least one curved surface forsupporting the string, the surface extending between an exit region forsaid string from said passageway and a peripheral region of the head,the head being characterized in that the passageway extends in a mannerthat is offset from an axis of rotation of the head so as to present aninside edge constituted by its edge closest to said axis of rotation,said inner edge corresponding to a trailing edge of the string while thehead is rotating, and in that the curved portion extends from said inneredge.

Certain preferred, but non-limiting, aspects of the cutting head are asfollows:

-   -   the string passageway is essentially rectilinear;    -   the string passageway is situated at a given distance from the        axis of rotation of the head, and the curved surface presents,        at least locally, a radius of curvature that is greater than        said distance;    -   the curved portion presents a radius of curvature that is        constant, or else variable;    -   the curved portion joins the string passageway, and/or the        peripheral region of the head, substantially tangentially;    -   a secondary curved portion is provided between an outer edge of        the passageway opposite from its inner edge and the peripheral        region of the head;    -   two string passageways and their respective curved portions are        provided;    -   the two string passageways are situated on either side of the        axis of rotation of the head, and the string outlets from the        respective passageways are situated in diametrically-opposite        regions of the head;    -   the cutter string presents a cross-section that is polygonal;        and    -   the cutter string presents a width greater than about 3 mm.

The invention also provides a vegetation cutting device such as a brushcutter, edge trimmer or similar, characterized in that it includes acutting head as defined above and a motor suitable for rotating saidcutting head.

Other aspects, aims and advantages of the present invention will appearmore clearly from the following detailed description of the preferredembodiments of the latter, given by way of non-limitative example andmade with reference to the appended drawings in which:

FIGS. 1 to 3 are three views in side elevation illustrating a cuttinghead according to one embodiment of the invention.

FIG. 4 is a plan view of a generally disc-shaped part constituting aportion of a cutting head according to the invention.

FIG. 5 is a profile view of two disc-shaped parts assembled to form thecutting head.

FIG. 6 is a profile view of a generally disc-shaped intermediate partthat can, with two other parts, form another cutting head according tothe invention.

FIG. 7 is a profile view of this other cutting head in the assembledstate.

FIG. 8 is a schematic plan view of the cutting head in FIG. 7, with fourstrands of cutting string mounted in the latter.

FIG. 8 a shows in perspective a curved bearing zone defined by thecutting head for one of the strands.

FIG. 9 illustrates a detail of the disc-shaped part in FIG. 4, fittedwith a device for locking a strand of string.

FIG. 10 is a view in cross-section along the line X-X in FIG. 9.

FIG. 11 is a cross-sectional view of a first variant of embodiment ofthe string locking device.

FIG. 12 is a view in perspective of a locking member belonging to thelocking device in FIG. 11.

FIG. 13 is a cross-sectional view of a second variant of embodiment ofthe string locking device.

FIG. 14 is a cross-sectional view of a third variant of the stringlocking device.

FIG. 15 is a plan view of a fourth variant of the string locking device,and FIG. 16 is a view in section along the line XVI-XVI in FIG. 15.

It will be noted as a preliminary matter that, from one figure to theother, the identical or similar elements or parts have, whereverpossible, been identified by the same reference marks.

FIGS. 1 to 3 represent a cutting head for a brush cutter, edge trimmerand similar according to the invention, globally identified by thereference 100, suitable for being mounted on the extremity of a driveshaft 200 provided for the purpose, fixing arrangements 202 (washer,nut, mechanism of indexation in rotation), as well as a counterplateintended to cooperate with the said fixing arrangements in a mannercompletely conventional in itself.

The cutting head is implemented here by overlaying and assembling twodisc-shaped parts 110 a and 110 b concentric with the axis of rotationof the drive shaft 200 and comprising, on their faces turned one towardsthe other, arrangements for running of strands of string and forretaining those strands as will be seen in detail below.

FIG. 1 illustrates the cutting head 100 before assembly to the shaft200, whereas FIGS. 2 and 3 illustrate, respectively in a view withpartial cutaway and a view in elevation, the cutting head mounted on theshaft.

With reference now to FIG. 4, this shows a disc-shaped part 110(possibly one of the parts 110 a and 110 b in FIGS. 1 to 3) contributingto the implementation of the cutting head. It is provided with a centralorifice 1100 through which the drive shaft 200 can pass.

This part 110 comprises a set of 450 bevels 111, 111′ (outer bevels) and111″ (central bevel) delimiting internally the portions of the part thatare raised and externally the portions of the part that are recess. Theoverall contour of the bevels is here circular and follows the contourof the disc, set back at a certain distance from this contour.

In particular, two bevels 111, 111″ extend in a rectilinear and adjacentmanner the one to the other to delimit a first zone 112 of cuttingstring strand passageway, this passageway opening onto the outside at afirst opening 113 and a second opening 115, for the outlet of a strandof a cutting string. The axis A along which the zone 112 extends issituated a certain distance, marked D, from the centre C of thedisc-shaped part.

At the opening 113, the radius of curvature of the bevels is small, itbeing simply to guide the strand of string when it is put in place.

At the string outlet 115, the bevel 111″ defines a curved bearing zone120, connected for preference without change of slope on the one handwith the string passageway zone 112 and on the other hand with thecircular peripheral zone formed jointly by the three bevels. This curvedbearing zone 120 supports the strand of string during cutting, inparticular when, when the cutting head rotates, it encounters obstaclesresisting cutting and causing it to give way (the direction of rotationof the cutting head being given by the arrow F). It is important to notehere, according to one aspect of the invention, that, due to the lateraloffset of the string passageway 112 in relation to the centre C of thepart 110, that is in relation to the axis of rotation of the cuttinghead, it is possible to give the curved bearing zone 120 a radius ofcurvature which is much greater than that which could be achieved, as inthe prior art, with a string passageway extending geometrically from thecentre C.

Specifically, in the case of the prior art, knowing that the centralzone of the cutting head is necessarily occupied by the shaft, verylittle room is available in the axial direction for implementing on theone hand the locking of the strand of cutting string, and on the otherhand the curved bearing surface.

On the contrary, due to the arrangement of the invention, a much greaterradius of curvature R can be envisaged and this can (at least locally)be equal to or even significantly greater than the distance D.

It will be noted here that the curved bearing zone may have any curvedgeometric shape required (circular, with circular sectors of differentradius, elliptical, parabolic, etc.). It will be understood inparticular that there may be one or more constant radii of curvature,and/or one radius of curvature varying continuously.

Due to a less pronounced curvature of the curved bearing zone, theactions are very considerably reduced as is the fatigue of the strand ofstring, because the material of the latter is much less stressed, andthis is particularly important with modern cutting strings comprisingarrangements (teeth, etc.) intended to facilitate cutting, and/orarrangements (recesses, protrusions, etc) intended to reduce noiseduring rotation, and/or zones of different materials (filled polyamides,etc.) intended for example to increase wear resistance.

The disc-shaped part 110 also comprises, on a section of the stringstrand passageway zone 112, a cavity 114 intended to receive a stringlocking shoe that will be described later. For the moment, mention willbe made here that this cavity opens out onto the string passageway zoneand comprises on the opposite side a vertical, unbevelled surfaceoriented at an angle relative to the axis A of the string passageway112, and also comprises, adjacent to the extremity of the surface 116furthest away from the axis A, a blind recess 117 intended for thewedging of a shoe pressure spring as will be seen in detail later.

Also represented in FIG. 4 are holes 118 suitable for being traversed byscrews or studs for the assembly of the part 110 with one or more otherdisc-shaped parts, designed in similar manner.

Finally, FIG. 4 shows that the part 110 comprises, with a symmetry ofrevolution of 180° relative to the arrangements described above, somesecond passageway, bearing and locking arrangements for a second strandof string, these arrangements being indicated by the same referencemarks plus a “prime” mark.

FIG. 5 shows in greater detail a cutting head implemented by assemblinga first disc-shaped part 110 a, comprising the arrangements asillustrated in FIG. 4, and a second disc-shaped part 110 b comprisingcorresponding arrangements, with a mirror symmetry, such that all thesearrangements are placed on top of their counterparts belonging to theother part 110 a during assembly.

It is understood that such an assembly forms string strand passagewaysin regular lozenge shape. By using strands of cutting string ofgenerally square cross-section and slightly smaller than thecross-section of the passageways formed in the head, these passagewaysretain the strands in an inclination such that it is a ridge of eachstring strand which will constitute a leading zone for cutting, to thusimprove cutting efficiency.

It will be observed however that such a head may be used with cuttingstring strands of any cross-section, provided that they can be engagedwithout being trapped in a string passageway.

It is understood that, on the basis of the arrangements as describedwith reference to FIG. 4, FIG. 5 implements a cutting head with twostrings situated at the same level in vertical direction and exitingfrom the head in an oblique direction relative to a strictly radialdirection, in two diametrically opposed places.

FIG. 6 illustrates in elevation another disc-shaped part 110 c,constituting a third intermediate part of the head.

This part 110 c comprises two sets of arrangements like thoserepresented in FIG. 4, respectively on each of its two faces, withpreferably a mutual offset of 900. One of these sets of arrangementsforms counterpart arrangements of those of the part 110 a, whereas theother of these sets of arrangements forms counterpart arrangements ofthose of the part 110 b. As a corollary, to fit the intermediate part110 c, the arrangements of the parts 110 a and 110 b are mutually offsetat a 90° angle.

It is understood that, in this way, a cutting head is implementedcomprising an upper level with two string strands with diametricallyopposed outlets, and a lower level with two other string strands withdiametrically opposed outlets also, but offset by 90° in relation to thefirst ones.

This cutting head is illustrated in elevation in FIG. 7. Shown in thisfigure are two openings, respectively 113 ac and 113 cb, offset at anangle of 90° and belonging respectively to the two levels, the openingsfor the outlet of the strings not having been represented in thisfigure.

It has been observed that such an arrangement of strings, with twolevels, advantageously provided chopping of the cut plant material whenthe distance between the planes of the string levels was well chosen.More particularly, and still with reference to FIG. 7, it has beenobserved that, if the distance H2 between the respective planes Pab andPbc of the two string levels is equal to or greater than approximately1.8 times the height H1 of a string (corresponding substantially to theheight of its passageway), and preferably equal to or less thanapproximately 5 times this same height H1, then particularlysatisfactory chopping is obtained. For example, with a string of squarecross-section with a side length of 4 mm, that is a diagonal measuringapproximately 5.6 mm, the height offset between the two cutting planesis greater than approximately 10 mm.

In such a configuration, chopping is equally favoured if, as describedabove, the string outlets are offset at an angle to one another. Forpreference, and as also described, this offset is such that, incircumferential direction, the string outlets are regularly spaced.

However, irregularly spaced string outlets (which is obtained inparticular if the angular offset between the arrangements of the upperlevel and those of the lower level is not 90°), a satisfactory result isalso obtained.

FIG. 8 represents a schematic view from above of the cutting head inFIG. 7. Installed in this cutting head are three strands of string 300which project at the string outlet 115 and which stop substantially atthe openings 113. Also represented in this figure are the curved bearingsurfaces 120 for the strands of string. The direction of rotation of thehead is illustrated by the arrow F.

In addition, it is understood in the light of the foregoing that byusing two intermediate parts of the type of part 110 c, or more, and twoterminal parts 110 a and 110, a head can be implemented with any numberof levels.

For example, by using an intermediate part that has its upper and lowerarrangements mutually offset by 60°, and by providing two of suchintermediate parts between the upper and lower parts 110 a, 110 b, athree-level cutting head is implemented with string outlets regularlydistributed in a circumferential direction.

FIG. 8 a illustrates in perspective the curved bearing surface 120formed by the head for one individual strand of string 300, representedby a part of its length.

It is understood that such a curved bearing surface is formed by thecurved bearing zones 120 a, 120 b of the two adjacent disc-shaped parts110 a and 110 b (in the case of a version such as the one in FIG. 5),which in turn belong to the 45° bevels 111″ of the respective parts.

This curved bearing surface therefore presents a V-shaped profile with a90° bottom angle, that is a profile suited to the cross-section of thestring 300 at the outlet of its passageway. Such a bearing surface istherefore used to retain the string in its optimal cutting orientationat all times, and in particular when, under the effect of resistancefrom the plants, it comes to rest against the bearing surface 120.

Naturally, the profile of the curved bearing surface will be adaptedaccording to the type of cross-section of the string. In this regard,even in the case of a string of circular cross-section, it can beenvisaged that the string rests on a curved bearing zone having arecessed circular profile. This minimizes the fatigue of the string andincreases the cutting efficiency by stabilizing its trajectory in thecutting plane when it comes to rest against the said zone. Inparticular, it avoids wasting kinetic energy in a direction transverseto the direction of cutting (vertical direction in use).

FIGS. 9 and 10 illustrate the string locking mechanism, mounted inside apair of disc-shaped parts (parts 110 a and 110 b in the basic form ofimplementation with a single cutting level). This mechanism comprises ashoe 400 placed in a housing defined by the cavity 114 formed in one ofthe disc-shaped parts (see FIG. 4), here 110 a, and by the counterpartcavity defined in the other disc-shaped part, here 110 b, which isjuxtaposed to it.

This shoe 400 possesses a first face possessing a plurality of teeth 404extending transversely to the axis A of the string passageway 112 andintended to bite into the cutting string 300 engaged in the saidpassageway 112, and an opposite face 402 extending at an oblique anglerelative to the abovementioned first face and intended to rest againstthe rear face of its housing, defined by the faces 116 of the twodisc-shaped parts.

A pressure spring 500 acts between a spring seat defined jointly by theblind recesses 117 of the two disc-shaped parts, and a recess 408 formedin a pressure region of the shoe 400, situated in the region of greatestheight of the said shoe.

On the opposite side (front side), the shoe possesses an inclinedsection 406 directed at an oblique angle towards the top from the tooth404 situated furthest forward.

The cutting strand of string 300, pre-cut to the required length, isengaged in its passageway 112 from its outlet opening 115, in thedirection of the arrow F′ in FIG. 9. Thus, it pushes back the shoe 400against the (moderate) force of the spring 500, the shoe thus being ableto rise by sliding against the rear face 116, 116 of its housing by theamount necessary to let the strand of string pass. The strand of stringis pushed preferably until its left-hand extremity in FIG. 9 reaches theregion of the opening 113, as illustrated in this same figure. Theoperator can thus ensure that the string has been fully engaged beyondthe locking shoe. It will be noted here that the inclined front section406 guides the strand of string so that it passes correctly under theshoe 400, on the toothed side.

It is well understood that, as soon as a pulling force is exerted on thestrand of string in the direction opposite to the arrow F′, which istypically the case when the device is working, by friction and impactsagainst the plants, the shoe 400, which actes as a one-way lock, tendsto exert on the strand of string 300, through its teeth 404, a retentionforce by gripping which is all the greater as the pulling forceincreases, this being so due to the inclined face 116, 116 of thehousing, providing a wedge effect in cooperation with the face 402 ofthe shoe.

Particular advantages of such a locking mechanism with sliding shoe, inparticular when compared with the known mechanisms with toothed cam orsimilar, reside on the one hand in that the retention force exerted onthe strand of string by the shoe, supported extremely firmly and solidlyby the rear surface 116, 116 of the shoe housing 114, 114, can beextremely strong and on the other hand in that the extent, according tothe length of the string 300, over which the teeth 404 cooperate withthe string, can be much greater than with a known cam mechanism.

Other advantages are (i) that the strand of string can be easilyinserted into the passageway through the opening 115 and easily removedfrom the passageway through the opposite opening 113, both being locatedat the periphery of the head, and (ii) that the locking mechanism can beplaced between the passageway 112 and the periphery of the head, i.e.without interfering with the central region of the head in which thearrangements (recess for shaft and nut) for mounting the head on thecutting device are to be positioned.

In the embodiment in FIGS. 9 and 10, and as is shown in FIG. 10, theteeth 404 retaining the strand of string extend in a rectilinear mannerin a direction transverse to the string.

According to another advantageous aspect, it can be envisaged that thestring strand locking element (moreover whether it is a sliding shoe, apivoting cam, or any other gripping element), is shaped in a manner toimprove the retention of the string.

Thus, while in FIGS. 9 and 10 the cooperation between the teeth 404 andthe string occurs simply at the level of the string ridge situatedopposite the shoe, it is envisaged, as illustrated in FIGS. 11 and 12,that the teeth adopt a profile suited to the shape of the string. Inthese figures, there are two series of teeth 404 a, 404 b oriented at90° to one another to form a profile comprising a recess 403. As aresult, each series of teeth may cooperate with a whole face, or asubstantial part of such a face, of a string in the case in point of asquare cross-section, and the extent of the cooperation between the shoeand the string to retain the latter is further increased.

More generally, any recessed profile can be envisaged at the level ofthe teeth of the shoe 400 to better receive the string, irrespective ofthe shape of the cross-section of the latter.

Thus FIG. 13 illustrates the case in which the region of the teeth ofthe shoe 400 has a profile with a central curved recess, and two seriesof teeth 404 a, 404 b of convex profile either side of this recess. Inthis case, it is primarily the double row of contact between the teethand the string which increases the gripping force.

It will be observed here that the locking shoes in FIGS. 11, 12 and 13have an improved string retention efficiency not only with a string ofsquare cross-section disposed as a lozenge, as described, but also withmany other cross-sections of string, and in particular a circularcross-section.

FIG. 14 for its part illustrates the case in which, with a cuttingstring 300 of circular cross-section, use is made of a row of teeth 404having a convexity suitable for receiving the string, with a radius ofcurvature of the string and a radius of curvature of the profile of theteeth preferably similar to one another.

It is understood that the use of the string locking element with arecessed profile zone of contact with the string applies not only to thecase of a shoe, but also to the case of an element of another type suchas a cam.

Thus FIGS. 15 and 16 illustrate the locking of a cutting string 300, inthis case of circular cross-section, with the aid of a cam 400 mountedon a pivot 401 and acted upon by a pressure spring 500. The teeth 404are disposed on a circular sector eccentric in relation to the axis ofrotation defined by the pivot 401.

It is observed in this embodiment that the cam has two rows of teeth 404a, 404 b generally straight in the extension of one another (see FIG.16), these two rows being separated by a central groove 403. Such aprofile of teeth here further improves the locking of the string withmany shapes of string.

Naturally, the present invention is not limited to the embodimentsdescribed and represented, and those skilled in the art will be able toprovide many variants and modifications.

Moreover, it is understood that the different aspects of the new cuttinghead described in the foregoing may most frequently be implementedindependently of one another or combined in different manners.

1. A cutting head for brush cutter, edge trimmer or similar, the headbeing of the type including a passageway (112) for a cutter string (300)and at least one curved surface (120) for supporting the string, thesurface extending between an exit region (115) for said string from saidpassageway and a peripheral region of the head, the head beingcharacterized in that the passageway extends (A) in a manner that isoffset from an axis of rotation (C) of the head so as to present aninside edge constituted by its edge closest to said axis of rotation,said inner edge corresponding to a trailing edge of the string while thehead is rotating, and in that the curved portion extends from said inneredge.
 2. A cutting head according to claim 1, characterized in that thestring passageway (112) is essentially rectilinear.
 3. A cutting headaccording to claim 2, characterized in that the string passageway (112)is situated at a given distance (D) from the axis of rotation (C) of thehead, and in that the curved surface (120) presents, at least locally, aradius of curvature (R) that is greater than said distance.
 4. A cuttinghead according to claim 1, characterized in that the curved portion(120) presents a radius of curvature that is constant.
 5. A cutting headaccording to claim 1 characterized in that the curved portion (120)presents a radius of curvature that is variable.
 6. A cutting headaccording to claim 1, characterized in that the curved portion (120)joins the string passageway (112) substantially tangentially.
 7. Acutting head according to claim 1, characterized in that the curvedportion (120) joins the peripheral region of the head substantiallytangentially.
 8. A cutting head according to claim 1, characterized inthat a secondary curved portion (122) is provided between an outer edgeof the passageway (112) opposite from its inner edge and the peripheralregion of the head.
 9. A cutting head according to claim 1,characterized in that two string passageways (112, 112′) and theirrespective curved portions (120, 120′) are provided.
 10. A cutting headaccording to claim 9, characterized in that the two string passageways(112, 112′) are situated on either side of the axis of rotation of thehead, and in that the string outlets (115) from the respectivepassageways are situated in diametrically-opposite regions of the head.11. A cutting head according to claim 1, characterized in that thecutter string (300) presents a cross-section that is polygonal.
 12. Acutting head according to claim 11, characterized in that the cutterstring (300) presents a width greater than about 3 mm.
 13. A vegetationcutting device such as a brush cutter, edge trimmer or similar,characterized in that it includes a cutting head according to claim 1and motor suitable for rotating said head.